The drilling of deep wells such as oil wells, and especially the drilling of offshore oil wells, is a very costly endeavor. For instance, the cost per day of operating an offshore drilling rig in comparatively shallow waters of 100 feet or less typically amounts to about $10,000 per day while the cost of operating a drilling vessel in deep waters exceeding depths of 200 feet can cost $30,000 per day or more.
It is manifest, therefore, that any interruption of the drilling operation will be very costly, and that it is highly desirable to avoid all but the most essential of drilling interruptions.
As indicated above, it is conventional practice to remove contaminating gases such as methane, air, carbon dioxide, etc., from drilling mud before it is pressured and injected into a well bore. If this is not done, there is an everpresent danger that the gas will accumulate in either the drill string or the well bore annulus in an amount sufficient to form a gas pocket.
Therefore, if a drilling mud degasser fails to operate properly, the drilling operation must be suspended until the drilling mud degasser is repaired.
Moreover, since drilling operations normally continue on an essentially continuous basis for 1 to 12 months or more, any part of the drilling mud degasser that does not have a design life of at least six months is apt to be the cause of an undesired and very expensive interruption of drilling operations.
Drilling mud degassers of the type shown in Burgess U.S. Pat. No. 4,084,946 require a motor, usually an electric motor, which operates a vacuum pump at one rate of speed and a centrifuge tube at another second lower rate of speed. In order to run both the centrifuge tube and the vacuum pump off a single drive shaft, it is necessary to utilize an appropriate gear reduction system, such as a planetary gear reduction system between the drive shaft and the centrifuge tube. Gear reduction systems such as planetary gear reduction systems are normally housed in a gear box.
Since appreciable friction is generated in the gear box during operations, it is necessary that the gear box at all times be properly lubricated with a lubricant which can stand the operating pressures employed. It has been the practice to use a grease, such as a high temperature grease able to withstand temperatures of about 250.degree. F. or more generated in the gear box. Moreover, the gear box needs to be greased on a daily basis and if for any reason the lubrication of the gear box is overlooked by workmen or if the gear box becomes overheated, a gear box failure is likely. When the gear box fails, drilling operations must be interrupted while the drilling mud degasser is taken apart to the extent necessary to replace the damaged gear box with a new gear box. Of course, if a spare gear box is not present on the vessel, an even greater delay will be experienced in bringing a gear box to the vessel. Although the down time of the degasser for the replacement of the gear box will normally be about 2 hours, the down time for the drilling rig will normally amount to 12 hours or more.
There is a need, therefore, for a self-lubricating drilling mud degasser which can operate without maintenance for prolonged periods of time such as about 1 to about 6 months.